
import java.math.*;
import java.util.Scanner;

import static java.lang.Math.floorDiv;
import static java.lang.Math.sqrt;

class Test{
    public static void main6(String[] args) {
        Scanner scanner=new Scanner(System.in);
        int a=scanner.nextInt();
        int b=scanner.nextInt();
        int c=scanner.nextInt();
        float f=((float)a+(float) b+(float) c)/3;
        System.out.print(a+b+c+" ");
        System.out.print(a*b*c+" ");
        System.out.printf("%.2f",f);
    }
    public static void main4(String[] args) {
        Scanner scanner=new Scanner(System.in);
        int x=scanner.nextInt();
        //scanner.nextLine();
        int y=scanner.nextInt();
        int tmp=0;
        tmp=x;
        x=y;
        y=tmp;
        System.out.println(x+" "+y);
    }
    public static void main3(String[] args) {
        Scanner scanner=new Scanner(System.in);
        float F=scanner.nextFloat();
        float C=5*(F-32)/9;
        System.out.printf("%.2f",C);
    }

    public static void main(String[] args) {

        Scanner scanner=new Scanner(System.in);
        double a,b,c;
        while(scanner.hasNext()){

            a=scanner.nextDouble();
            b=scanner.nextDouble();
            c=scanner.nextDouble();
            boolean det=(a<=0||b<=0||c<=0)?false:true;
            if((a+b)<=c) det=false;
            else if((a+c)<=b) det=false;
            else if((b+c)<=a) det=false;


            if(det==true){
                double p=(a+b+c)/2;
                double s=p*(p-a)*(p-b)*(p-c);
                System.out.printf("%.2f\n",sqrt(s));
            }
            else{
                //System.out.println();
                System.out.printf("Input Error!\n");
            }
        }
    }
    public static void main1(String[] args){
        Scanner scanner=new Scanner(System.in);
        byte byte1=scanner.nextByte();
        short short1=scanner.nextShort();
        int int1=scanner.nextInt();
        long long1=scanner.nextLong();
        float float1=scanner.nextFloat();
        double double1=scanner.nextDouble();
        scanner.nextLine();
        String string1=scanner.nextLine();
        String[] strings={"byte","short","int","long","float","double"};
        System.out.println("byte:"+byte1);
        System.out.println("short:"+short1);
        System.out.println("int:"+int1);
        System.out.println("long:"+long1);
        System.out.println("double:"+double1);
        System.out.println("float:"+float1);
        System.out.println("String:"+string1);


//        System.out.println(1+1.0);
    }
}


